In multi carrier-code division multiple access (MC-CDMA), there is a method for spreading to a frequency domain. In this method, after the information data stream is spreaded with a given spreading code series, each chip is mapped to different subcarriers. FIG. 1 is a schematic diagram showing a packet configuration of the MC-CDMA conducting a frequency domain spreading. Here, a primary-pilot channel (P-PICH) is shown with oblique lines, a dedicated-pilot channel (D-PICH) with halftone dot meshing, and dedicated physical channel (DPCH) with white background. The P-PICH is a pilot for a cell searching and a synchronized tracking, and the D-PICH is a pilot employed for SIR estimation for adaptive radio parameter control, channel estimation of the DPCH and Doppler frequency estimation.
In these packets shown in this figure, one frame (54 symbols) is composed of two slots. In one frame, P-PICH, D-PICH and DPCH are time division-arranged. As can be seen from the figure, four symbols are arranged in one frame for the D-PICH.
Conventionally, in order to ideally conduct a control such as adaptive modulation or a resource allocation, it is necessary to appropriately measure the quality of received signal, and noise power maybe employed as a quality of received signal. The noise power includes a thermal noise generated inside a receiver and a noise generated by an interference of the other cell through the propagation path. The D-PICH having the above-described packet configuration is employed for the estimation of the noise power (referred to as “N+Iother”) per one frame. Conventional estimation for the noise power (“N+Iother”) is described as follows.
FIG. 2 is a block diagram showing a configuration of a conventional receiving system. In this figure, radio processing section 11 receives signal transmitted from a communication partner through an antenna, and predetermined radio processing such as down conversion and AD conversion is conducted on the received signal, and radio processed signal is output to GI removal section 12. The GI removal section 12 eliminates guard interval of signal that is output from the radio processing section 11, and the processed signal is output to a FFT section 13. The FFT section 13 acquires signal, which is transmitted on each subcarrier by conducting fast Fourier transform for signal output by the GI removal section 12. The acquired signals at each of subcarriers are output to a pilot extract section 14.
Pilot extract section 14 extracts time multiplexed pilot channel (PICH) from a signal of each of subcarriers that is output from the FFT section 13, and the extracted PICH is output to a noise power estimation section 15. On the other hand, signal excluding PICH is output to P/S converter 16.
The noise power estimation section 15 estimates noise power on the basis of PICH that is output from the pilot extract section 14. Details of the noise power estimation section 15 will be described later.
P/S converter 16 conducts P/S conversion processing for signal excluding PICH that is output from the pilot extract section 14 and output P/S converted signal to a despreading section 17. The despreading section 17 conducts a despread processing by multiplying a predetermined spread code to the P/S converted signal and output despreaded signal to a demodulating section 18. The demodulating section 18 conducts demodulating processing for despreaded signal that is output from the despread section 17, and output them to a decoding section 19. The decoding section 19 conducts a decoding processing such as turbo decoding and the like to signal that is output from the demodulating section 18, and output them to an error detecting section 20. The error detecting section 20 conducts an error detection of signal that is output from the decoding section 19, and output data if error is not detected.
FIG. 3 is a block diagram showing an internal configuration of the noise power estimation section 15 in a conventional apparatus. Adder 21 calculates pilot symbol correlated/in-phase added value (ξi) of a subcarrier i in time orientation using PICH that is output from the pilot extract section 14, and output the calculation results of each of subcarriers to a delay device 22-1 (shown as “D” in figure) and a multiplier 23-1.
The delay device 22-1 delays ξ of respective subcarriers that are output from the adder 21 until next ξ is input, and the obtained ξ is output to a delay device 22-2 and a multiplier 23-2. These operations are similarly applied to delay devices 22-2 to 22-4, and these delay devices delays ξi−2 to ξi+1 that are output from the adder 21 (i is defined to be within a range of from 0 to 767) by one, respectively, to output ξ to multipliers coupled to each of the delay devices. However, there is no output from the delay device 22-2 to the multiplier. In this case, it is assumed that 768 subcarriers are employed, and delay processing is conducted for 768 ξs.
The multipliers 23-1 to 23-4 contains predetermined coefficients that are logically calculated beforehand, and respective predetermined coefficients are multiplied to ξ that are respectively input, and is output to the adder 24. The adder 24 adds four ξ input therein, and outputs to a square device 25. The square device 25 calculates squares of values that are output from the adder 24 to calculate the noise powers of respective subcarriers. A cumulative adder 26 performs cumulative-addition on noise powers of respective subcarriers that are output from the square device 25, and output the results of the cumulative-additions to a multiplier 27. Multiplier 27 multiplies predetermined coefficients to the added values that are output from the cumulative adder 26 to calculate “N+Iother”.
FIG. 4 is a diagram, showing PICH with its relation between time and subcarrier. In this figure, the vertical axis indicates numbering of subcarriers (subcarrier i: i=0 to Nc−1), the horizontal axis indicates time, and PICH is shown as ri,j. Here, Nc is number of the employed subcarriers. The signs ri,j is a correlation value of received signal of PICH symbol j of subcarrier i, and scramble code and pilot symbol pattern are removed therefrom. For example, PICH transmitted from subcarrier 1 are r1,0, r1,1, r1,2, r1,3.
In the next, an arithmetic operation conducted within the noise power estimation section 15 will be described using formulas. In the adder 21, pilot symbol correlated/in-phase added values in time orientation (ξ) is obtained for respective subcarriers by using ri,j. More specifically, the values are obtained by the following formula:
                              [                      formula            ⁢                                                  ⁢            1                    ]                ⁢                                  ⁢                                  ⁢                              ξ            i                    =                                    1              4                        ⁢                                          ∑                                  j                  =                  0                                3                            ⁢                              r                                  i                  ,                  j                                                                                        (        1            
Alternatively, ξi can be represented by ξi=hi+ni, by using noise component ni and channel variation component hi. ξi calculated in the adder 21 is transmitted to delay devices 22-1 and multiplier 23-1 consecutively.
We will specifically find out “N+Iother” by focusing on subcarrier i as follows. Here, a case of using ξ averaged for two adjacent subcarriers for calculating noise power per one subcarrier will be described:
                              [                      formula            ⁢                                                  ⁢            2                    ]                ⁢                                  ⁢                                  ⁢                              ɛ                          i              -              0.5                                =                                                    1                2                            ⁢                              (                                                      h                                          i                      -                      1                                                        +                                      n                                          i                      -                      1                                                                      )                                      +                                          1                2                            ⁢                              (                                                      h                    i                                    +                                      n                    i                                                  )                                                                        (        2                                          [                      formula            ⁢                                                  ⁢            3                    ]                ⁢                                  ⁢                                  ⁢                              ɛ                          i              +              0.5                                =                                                    1                2                            ⁢                              (                                                      h                    i                                    +                                      n                    i                                                  )                                      +                                          1                2                            ⁢                              (                                                      h                                          i                      +                      1                                                        +                                      n                                          i                      +                      1                                                                      )                                                                        (        3            
Here, εi−0.5 and εi+0.5 are the averaged values of respective ξ of subcarrier number i−1 and i and subcarrier number i and i+1. Assuming that the condition is free of noise and the correlation between adjacent subcarriers is 1, the value obtained by subtracting εi+0.5 from εi−0.5 becomes zero. Therefore it is considered that the values obtained as differences are noise component. The noise power for subcarrier i is found by squaring the noise component thus obtained. More specifically, it can be expressed by the following formula (4):
[formula 4]σi=|εi−0.5−εi+0.5|2  (4
The following formula (5) can be derived from formula (2) and formula (3):
                              [                      formula            ⁢                                                  ⁢            5                    ]                ⁢                                  ⁢                                  ⁢                              σ            i                    =                                                                                                        1                    2                                    ⁢                                      (                                                                  h                                                  i                          -                          1                                                                    -                                              h                                                  i                          +                          1                                                                                      )                                                  +                                                      1                    2                                    ⁢                                      (                                                                  n                                                  i                          -                          1                                                                    -                                              n                                                  i                          +                          1                                                                                      )                                                                                      2                                              (        5            
In this case, correlations between adjacent subcarrier waves are not necessarily be 1 for subcarriers i−1 to i+1, and thus there may be a case that a difference in channel variation h is generated. In other words, since the value obtained by subtracting hi+1 from hi−1 is not zero, error is generated for σi that is wanted to be found. Therefore, a correction is done in order to diminish error generated by channel variation to obtain the following formula (6):
                              [                      formula            ⁢                                                  ⁢            6                    ]                ⁢                                  ⁢                                  ⁢                              σ            i            ′                    =                                                                                                        1                    2                                    ⁢                                      (                                                                  h                                                  i                          -                          1                                                                    -                                              h                                                  i                          +                          1                                                                                      )                                                  +                                                      1                    2                                    ⁢                                      (                                                                  n                                                  i                          -                          1                                                                    -                                              n                                                  i                          +                          1                                                                                      )                                                  -                                                      1                    2                                    ⁢                                      (                                                                                            h                          ^                                                                          i                          -                          1                                                                    -                                                                        h                          ^                                                                          i                          +                          1                                                                                      )                                                                                      2                                              (        6            
Here, h^i−1 is a value obtained by averaging ξ for the plurality of subcarriers adjacent to subcarrier i−1, and can be obtained by the following formula (7):
                              [                      formula            ⁢                                                  ⁢            7                    ]                ⁢                                  ⁢                                  ⁢                                                                                                  h                    ^                                                        i                    -                    1                                                  =                                ⁢                                                      1                    2                                    ⁢                                      (                                                                  ɛ                                                  i                          -                          1.5                                                                    +                                              ɛ                                                  i                          -                          0.5                                                                                      )                                                                                                                          =                                ⁢                                                      1                    2                                    ⁢                                      {                                                                                            1                          2                                                ⁢                                                  (                                                                                    h                                                              i                                -                                2                                                                                      +                                                          n                                                              i                                -                                2                                                                                                              )                                                                    +                                                                        1                          2                                                ⁢                                                  (                                                                                    h                                                              i                                -                                1                                                                                      +                                                          n                                                              i                                -                                1                                                                                                              )                                                                    +                                                                        1                          2                                                ⁢                                                  (                                                                                    h                                                              i                                -                                1                                                                                      +                                                          n                                                              i                                -                                1                                                                                                              )                                                                    +                                                                                                                                                              ⁢                                                      1                    2                                    ⁢                                      (                                                                  h                        i                                            +                                              n                        i                                                              )                                                  }                                                                                        =                                ⁢                                                      1                    4                                    ⁢                                      (                                                                  h                                                  i                          -                          2                                                                    +                                              2                        ⁢                                                  h                                                      i                            -                            1                                                                                              +                                              h                        i                                            +                                              n                                                  i                          -                          2                                                                    +                                              2                        ⁢                                                  n                                                      i                            -                            1                                                                                              +                                              n                        i                                                              )                                                                                                          (        7            
On the other hand, h^i+1 is obtained by the following formula (8):
                              [                      formula            ⁢                                                  ⁢            8                    ]                ⁢                                  ⁢                                  ⁢                                                                                                  h                    ^                                                        i                    +                    1                                                  =                                ⁢                                                      1                    2                                    ⁢                                      (                                                                  ɛ                                                  i                          +                          0.5                                                                    +                                              ɛ                                                  i                          +                          1.5                                                                                      )                                                                                                                          =                                ⁢                                                      1                    4                                    ⁢                                      (                                                                  h                        i                                            +                                              2                        ⁢                                                  h                                                      i                            +                            1                                                                                              +                                              h                                                  i                          +                          2                                                                    +                                              n                        i                                            +                                              2                        ⁢                                                  n                                                      i                            +                            1                                                                                              +                                              n                                                  i                          +                          2                                                                                      )                                                                                                          (        8            
In this way, h can more precisely be found by conducting the averaging operation using ξ across a plurality of subcarriers, thereby diminishing an error of σi. Formula (7) and formula (8) are substituted into formula (6) to obtain formula (9) shown below:
                              [                      formula            ⁢                                                  ⁢            9                    ]                ⁢                                  ⁢                              σ            i            ′                    =                                                    (                                  1                  8                                )                            2                        ⁢                                                                                                -                                          (                                                                        h                                                      i                            -                            2                                                                          -                                                  h                          i                                                                    )                                                        +                                      2                    ⁢                                          (                                                                        h                                                      i                            -                            1                                                                          -                                                  h                                                      i                            +                            1                                                                                              )                                                        -                                      (                                                                  h                        i                                            -                                              h                                                  i                          +                          2                                                                                      )                                    -                                      n                                          i                      -                      2                                                        +                                      2                    ⁢                                          n                                              i                        -                        1                                                                              -                                      2                    ⁢                                          n                                              i                        +                        1                                                                              +                                      n                                          i                      +                      2                                                                                                  2                                                          (        9            
Here, assuming that differences of respective channel variation components are equal, i.e., hi−1−hi+1=hi−2−hi=hi−hi+2=Δ, the relationship of the following formula (10) is satisfied:
[formula 10]2Δ=2(hi−1−hi+1)=(hi−2−hi)+(hi−hi+2)  (10
Formula (11) is provided by conducting an approximating calculation of formula (9) using formula (10):
                              [                      formula            ⁢                                                  ⁢            11                    ]                ⁢                                  ⁢                                  ⁢                              σ            i            ′                    =                                                    (                                  1                  8                                )                            2                        ⁢                                                                                                -                                          n                                              i                        -                        2                                                                              +                                      2                    ⁢                                          n                                              i                        -                        1                                                                              -                                      2                    ⁢                                          n                                              i                        +                        1                                                                              +                                      n                                          i                      +                      2                                                                                                  2                                                          (        11            
Formula (11) presents an arithmetic operation conducted in the square device 25, and, in practice, calculation is carried out by replacing n with ξ.
                              [                      formula            ⁢                                                  ⁢            12                    ]                ⁢                                  ⁢                                  ⁢                              σ            i            ′                    ⁢                                          =                                          ⁢                                                    (                                  1                  8                                )                            2                        ⁢                                                  ⁢                                                                                                -                                          ξ                                              i                        -                        2                                                                              +                                      2                    ⁢                                                                                  ⁢                                          ξ                                              i                        -                        1                                                                              -                                      2                    ⁢                                                                                  ⁢                                          ξ                                              i                        +                        1                                                                              +                                      ξ                                          i                      +                      2                                                                                                  2                                                          (        12            
In this formula, coefficients of respective ξ are the coefficients that are set by multipliers 23-1 to 23-4, respectively. In other words, a part of the calculation using formula (12) is conducted in these multipliers. The results by the calculation within the square device 25 is output to the cumulative adder 26. Thus, provided that ni−2 to ni+2 satisfy probability distribution of Gaussian distribution in formula (11) and average power is presented as (na)2, it can be expressed by formula (13):
                              [                      formula            ⁢                                                  ⁢            13                    ]                ⁢                                  ⁢                                  ⁢                              σ            i            ′                    ⁢                                          =                                          ⁢                                                                      (                                      1                    8                                    )                                2                            ·              9                        ⁢                                          (                                  n                  a                                )                            2                                                          (        13            
Assuming that α=(⅛)2 (9), the noise power (“N+Iother”) can be presented as:
                    [                  formula          ⁢                                          ⁢          14                ]                                                                      N          +                      I            other                          =                                            4              α                        ·                                          (                                                      σ                    2                    ″                                    +                                      σ                    3                    ″                                    +                                                            σ                      4                      ″                                        ⁢                    ⋯                                    +                                      σ                                                                  N                        c                                            -                      3                                        ″                                                  )                            /                              N                c                                              -          4                                    (        14            
In this case, cumulative-adding operation for σ′ that is output from the square device 25 is conducted in the cumulative adder 26, and 4/((Nc−4)×α) are multiplied thereto in the multiplier 27, thereby providing an estimation of “N+Iother”. Here, the reason of multiplying 4 thereto is to reflect the value into noise power per one frame (“N+Iother”), as ξ is obtained by conducting the averaging operation using four pilot symbols. In addition, the reason of dividing by (Nc−4) is that number of cumulative-added σ′ is given by (Nc−4), and thus conducting the average operation is intended.
Estimations of noise power has conventionally been carried out by the method stated above.
However, in the above-described conventional process for estimating noise power, there is a problem, in which noise power cannot be precisely estimated when the channel variations in respective subcarriers are large by the influence of frequency selectivity fading or the like.